It's easy, today, to think of the space programs as normal, and orbital launches routine, when private companies like SpaceX and Orbital ATK share the sky with NASA and Roscosmos. But not so long ago, piercing the heavens atop a repurposed nuclear bomb delivery system was the thrilling, risky stuff of science fiction.
The first U.S. and Soviet rockets used for space exploration began their lives as nuclear missiles. They went through many catastrophic failures before they got to the point of sending people into space. Their warheads swapped for astronaut capsules, the rockets required new systems for safety and reliability that weapons did not require. It was ingenuity pitted against the unexplored to become the first in the race for Space.
And as NASA developed and modified rockets for the unknowns of space travel, astronauts were trained for the unknown, too, enduring those accidents and other mishaps for the chance to ride atop modified Redstone and Atlas ballistic missiles to the atmosphere.
The first human in space, Yuri Gagarin, rode atop a Vostok-K rocket, derived from the R-7, the first intercontinental ballistic missile. The Soyuz spacecraft that now shuttle crews to and from the International Space Station still make the trip atop rockets derived from the R-7.
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The first American to follow in Yuri Gagarin's wake above the sky, Alan Shepard, flew the Freedom 7 on a sub-orbital flight atop a Mercury-Redstone rocket. Shepard would eventually ride the mighty Saturn V rockets to the moon.
On the third crewed U.S. space flight, John Glenn, who died Thursday at 95, flew the capsule Friendship 7, which rode atop a larger Mercury-Atlas rocket in 1962 to orbit the earth three times. Glenn returned to space aboard the space shuttle in 1998, when he was 77.
This exploration itself was full of risk for the astronauts navigating it — but creating the technology that made that exploration happen was full of its own risks on the ground, too. Ground crews worked with toxic and volatile chemicals that were successful in blasting rockets into space, but required a constant vigilance on the ground.
Technological wonders of complex mathematics and computer systems made the rocket flights possible, but a human touch provided reassurance for the explorers themselves. According to NASA, scientist Katherine Johnson, who provided the trajectory analysis for Shepard's Freedom 7 flight, provided Glenn with the reassurance that the electronic calculations for his own orbit of the Earth were indeed correct:
As a part of the preflight checklist, Glenn asked engineers to "get the girl" — Katherine Johnson — to run the same numbers through the same equations that had been programmed into the computer, but by hand, on her desktop mechanical calculating machine. "If she says they're good,'" Katherine Johnson remembers the astronaut saying, "then I'm ready to go."
Johnson went on to work on the Apollo program and continue work at NASA into the 1980s. She was awarded the Presidential Medal of Freedom in 2015.
By the time Glenn became the first U.S. astronaut to orbit the Earth, the Mercury program alone had launched 20 crew-less missions, attempting feats that had never before been done: They left the atmosphere. They tested emergency escape systems.
Eventually, the Mercury program set the stage for the Gemini program — which paved the trail toward Apollo, whose astronauts would ride atop the gargantuan Saturn rockets and to the Moon.
The Apollo program was the first to send a crew outside Earth's orbit, and its rockets marked another transition: Astronauts would no longer ride atop repurposed machines of war, but instead atop machines built specifically for exploration.
The Mercury Seven — Alan Shepard, Gus Grissom, John Glenn, Scott Carpenter, Wally Schirra, Gordon Cooper and Deke Slayton — pioneered the idea that American astronauts would ride missiles into the sky in the name of exploration. They opened the door to the manned space age and scientific exploration into the darkness of space.